1. Field of the Disclosure
This specification relates to a nitride semiconductor device and a fabricating method thereof.
2. Background of the Disclosure
An importance of power semiconductor is rising in response to an emphasis of green energy. Power semiconductors which are employed in inverters of electric vehicles, air conditioners, refrigerators and the like are fabricated using silicon. However, a new type of nitride semiconductor attracts attentions in view of a high threshold electric field, low on-resistance, and high temperature and high frequency operation characteristic, as compared with silicon. Thus, there are precedent researches for the new type of nitride semiconductor as a material of a next-generation power semiconductor device.
In recent time, mainstream high power devices include MOSFET and IGBT, and also devices such as GaN-based HEMT, HFET, MOSFET and the like are under studies.
The HEMT which uses high electron mobility is employed for communication devices exhibiting high frequency performance.
Also, the HEMT is used in power semiconductors, communication devices showing high frequency performance, and the like. In recent time, developments of hybrid/fuel cell cars are ongoing, and various overseas corporations are releasing hybrid vehicles. Reliable operations at high temperature are required for semiconductor switches, which are disposed within voltage booster converter and inverter for connecting a motor to a generator within a hybrid vehicle, due to heat generated from an engine. Gallium nitride (GaN) may allow for the reliable operations at the high temperature owing to its wide bandgap, so as to be proper as the next generation semiconductor switch within hybrid cars.
Among others, Furukawa Electrics in Japan has issued an AlGaN/GaN high-electron-mobility transistor (HEMT) discrete, which has a high breakdown voltage of 750V and a low on-resistance of 6.3 mΩ-cm2. The company has thusly proved that the HEMT has superior characteristics to the conventional Si MOSFET, Si superjunction MOSFET and SiC MOSFET. Also, the issued GaN discrete has shown a stable switching operation at a high temperature of 225° C.
FIG. 1 is an exemplary view showing a general structure of Heterojunction Field Effect Transistor (HFET).
As shown in FIG. 1, a general HFET 10 may switch a 2 DEG current, which flows from a drain electrode to a source electrode, through a schottky gate electrode.
The general HFET 10 may include a substrate (not illustrated), a first GaN layer 11 formed on the substrate, an AlGaN layer 12 on the first GaN layer 11, a second GaN layer 13 on the AlGaN layer 12, and a gate electrode 14, a source electrode 15 and a drain electrode 16 all formed on the second GaN layer 13.
However, when the high-power semiconductor device is implemented on a small chip, a problem relating to a leakage current level is getting more important to handle.
That is, upon fabricating the AlGaN/GaN HEMT, a leakage current increases due to defective GaN, which accordingly makes it difficult to produce a high-power nitride semiconductor device.
To improve a leakage current characteristic, a growth condition of a GaN buffer layer is used. The use of the growth condition of the GaN buffer layer brings about a reduction of the leakage current, but the reduction of the leakage current may cause a direct affection on strain and quality of an epitaxial (Epi) layer.